Abstract: This invention relates to a process for setting up several data paths on a single optical transmission fiber, including a modulation step consisting, for each data path, of modulating a light source with a specific wave length by signals corresponding to said data path, a step transmitting the modulated light signals to a mixer and a step of chromatically separating the light signals transmitted by the optical fiber, characterized in that the signals are multiplexed by an integrating sphere coated on the inside with a reflecting surface and including a plane reflector oriented perpendicular to the axis of the transmission optical fiber.